1. Field of the Invention
The present invention relates to an analog signal amplifying method in the field of a digital amplifier and more particularly to an analog signal amplifying method that restrains the distortion degree of output waveform to significantly improve output of audio amplifier or the like. Also, the present invention relates to an integrated circuit of an amplification device made by using such an amplifying method. Furthermore, the present invention relates to an amplifier that utilizes various digital data signals like pulse width modulation (PWM) signals or pulse code modulation (PCM) signals as input signals. And finally, the present invention relates to a sawtooth-wave oscillator and a power amplification device used for a variety of amplifiers.
2. Brief Description of the Prior Art
In general, an amplification device of an audio amplifier has mostly been made of transistors. However, there have been critical problems in the general amplification devices using transistors in that the magnitude of allowable input bias voltage thereof (generally called base voltage) is relatively lower (generally, less than 0.6 V). In other words, in the case of transistors, a desired value of an output (generally, collector current or voltage) can be properly obtained only when the base input voltage is less than the allowable input voltage. However, there may be a significant waveform distortion when the base input voltage is over 0.6 V. FIG. 3a illustrates a normal output of transistors when the base input voltage is less than 0.6 V (In the drawing, the curve corresponds to a waveform of an output current. But when load resistance is connected with the amplification device, the output current transforms into output voltage corresponding thereto). FIG. 3b illustrates waveform distortion of an output signal when the base input voltage is over 0.6 V.
In order to solve the problem like the aforementioned waveform distortion of a desired output caused by unbalance of the input bias voltage, there has been a method of compensating an input bias voltage by letting some part of the output signals in reverse phase go back to the input through a negative feedback circuit. However, this method has another problem in that the input waveform compensated by feedback of output results in distortion due to a time delay (Td) for passing through the negative feedback circuit (shown in FIG. 4c), and therefore, the resultant output waveform also has distortion. FIGS. 4a and 4b are typical examples of amplifiers that compensate the input bias voltage. FIG. 4c illustrates a distortion type of an input waveform in which an input waveform and a negative feedback waveform are combined and a distortion type of an output waveform corresponding to the distortion type of the input waveform. In case of the amplifier circuits using the negative feedback compensation method, the numbers of amplification stages are relatively larger because of the lower gain degree thereof and the degree of waveform distortion in output side increase in proportion to the number of amplification stages.
Meanwhile, a field effect transistor (FET) having a gate voltage of about 1.5 V can be utilized as a means for compensating the narrower range of bias input voltage of a transistor. However, FET has been used only for a few particular circuits because of its operational instability affected by a temperature change and its own characteristic error.
A conventional vacuum tube amplifier has a bias voltage of over 1.5 V and a big amplification gain, so that it has a small number of amplification stages. Since there is little distortion of cross modulation in the audio amplifying circuit using a vacuum tube, it can be frequently witnessed that professional music specialists appreciate music with a vacuum tube amplifier. In spite of such an advantage, the vacuum tube amplifier has lost its practicality at present because of the its disadvantages such as high power consumption, large bulkiness in size, deterioration in sound quality and higher costs in manufacturing and maintenance.
On the other hand, there is an audio amplifier called a xe2x80x9cclass-D amplifierxe2x80x9d of digital circuit using a pulse width modulation (PWM) method that keeps the merits but compensates the demerits of the aforementioned vacuum tube. FIG. 5 illustrates an instance of a xe2x80x9cclass-D amplifier.xe2x80x9d As shown in FIG. 5, the class-D amplifier has a sawtooth-wave oscillator built-in on it. A comparator COMP6 compares sawtooth-wave voltage W1 with input signal Vi6 and determines an output W2 as HIGH while the input signal Vi6 is higher than the sawtooth-wave voltage W1 (Refer to Q in FIG. 6). The square-waves have pulse widths which have been converted In response to the change in magnitude between the input signal and sawtooth-wave (PWM modulation). An output (W2) of the aforementioned comparator switches MOSFET at an output terminal (W3) (refer to solid line shown in FIG. 6). At this time, the output signal (W3) is a square-wave resulting from ON/OFF switching of supply voltage supplied to the output terminal, so that it contains a lot of harmonic waves and its duty rate changes according to the magnitude of an input voltage. The output signal (W3) has a higher level of average voltage if an ON signal has a big width, but has a lower level of average voltage if the ON signal has a small width (refer to dotted line shown in FIG. 6). The output signal (W3) is passed to a low pass filter (LPF) for integration. The harmonic waves are eliminated to obtain the resultant analog output signal (Refer to S shown in FIG. 6).
However, there have been problems in the xe2x80x9cclass-D amplifierxe2x80x9d in that LC filter should be connected in multi-stages to smoothen the output signal, square-wave (that is, to eliminate elements of a harmonic wave), thereby resulting in a large bulkiness of coils and requiring advanced skill for shutting off electronic waves emitted from the outside. Also, there Is still another problem in the xe2x80x9cclass-D amplifierxe2x80x9d in that the sawtooth-wave oscillation frequency should be raised to the maximum level of frequency that can switch MOSFET for a high level of sound quality, thereby requiring advanced filtering and switching skills.
It is an object of the present invention to solve the aforementioned problem and provide a simple and easily manufactured analog signal amplifying method, which eliminates the distortion of an output waveform to generate the resultant output similar to an original sound or original analog signal but needs neither multi-step filters to have only a small bulkiness in size nor advanced filtering and switching skills. It is also an object of present invention to provide an amplification device integrated with a semiconductor using the analog signal amplifying method.
It is another object of the present invention to provide an amplifier to input digital data signals such as PWM signals in a combination of digital device such as a modernized CDP or the like and a power amplifier to solve a lot of problems occurring at the D/A conversion step by omitting an intermediate D/A conversion process but directly connecting digital data.
It is still another object of the present invention to provide a sawtooth-wave oscillator to be used for the amplifier or amplification device.
It is further another object of the present invention to provide a power amplification device to be used for the amplifier or amplification device.
In order to accomplish the aforementioned object of the present invention, there is provided an analog signal amplifying method of an analog signal amplifier in accordance with a first characteristic structure, the method comprising the steps of;
outputting a first sawtooth-wave having a frequency much larger than a maximum frequency of input signal of the amplifier, an amplitude identical to or a little larger than a maximum amplitude of the input signal and a predetermined period;
comparing the first sawtooth-wave with the input signal to output a first pulse of high level while amplitude of the first sawtooth-wave is larger than that of the input signal;
outputting a second pulse having a small width in the form of one short type at every starting point of high level region of the first pulse;
outputting a second sawtooth-wave having an amplitude identical to or a little larger than a maximum amplitude of output signal of the amplifier and the same period and phase as that of the first sawtooth-wave;
corresponding the respective starting points of high level regions of the second pulse to the second sawtooth-wave to continuously generate an output voltage on the basis of the second sawtooth-wave voltage positions where the starting points and the high level regions are corresponded with each other; and
charging the generated voltage into a condenser by a high speed switch, keeping constantly the charged voltage In it and eliminating a valley of the output waveform to be easily filtered.
In order to accomplish the aforementioned object of the present invention, there is provided an analog signal amplifying method of an analog signal amplifier in accordance with a second characteristic structure, the method comprising the steps of:
outputting a first sawtooth-wave having a frequency much larger than a maximum frequency of the input signal of the amplifier, an amplitude identical to or a little larger than a maximum amplitude of the input signal and a predetermined period;
comparing the first sawtooth-wave with the input signal to output a first pulse of high level while the amplitude of the first sawtooth-wave is larger than that of the input signal;
outputting a second pulse having a small width in the form of one short type at every starting point of high level regions of the first pulse;
outputting a second sawtooth-wave having an amplitude identical to or a little larger than a maximum amplitude of output signal of the amplifier and the same period and phase as that of the first sawtooth-wave;
corresponding the respective starting points of high level regions of the second pulse to the second sawtooth-wave to continuously generate a first output voltage on the basis of the second sawtooth-wave voltage position where the starting points and the high level regions are corresponded with each other;
outputting a third sawtooth-wave having reversed phase of the second sawtooth-wave;
corresponding the respective starting points of high level regions of the second pulse to the third sawtooth-wave to continuously generate a second output voltage on the basis of the third sawtooth-wave voltage position where the starting points and the third sawtooth-wave are corresponded with each other;
charging the first and second generated voltage into a condenser by an analog switch, constantly maintaining the voltage charged in it and eliminating valleys of the output waveforms to be easily filtered; and
obtaining a double magnitude of output signal by utilizing the first and second outputs.
In order to accomplish the aforementioned object of the present invention in accordance with a third characteristic structure, as defined in the first or second characteristic structure, there is additionally provided a method including a step of adjusting gain of an amplifier by adjusting the amplitude of the first sawtooth-wave.
In order to accomplish the aforementioned object of the present invention in accordance with a fourth characteristic structure, as defined in the first or second characteristic structure, there is additionally provided a method including a step of modulating the amplitude of the input signal by adjusting the amplitude of the first sawtooth-wave through a second input signal apart from the input signal.
Furthermore, it is an object of the present invention to provide an amplification device integrated with a semiconductor using the first through fourth characteristic structures.